Much research was done on motion sensing that is based on blocking and reflection of radio waves. An object that is located somewhere along the propagation path of a radio signal may affect the overall propagation path of the signal, as it may attenuate, block, or reflect certain parts of the signal. In a multipath environment, a receiver that is tuned to receive the said radio signal receives the superposition of all signal paths—resulting in possible decay or intensification of the signal amplitude depending on the phase of each individual component. Those specific signal components that are affected by a given object may change their phases and amplitudes depending on the position of the object. By inspecting the changes in the received signal amplitude the receiver may be able to determine whether or not there is any object in motion in the close environment. Motion sensing that is based on radio signals consist of a radio transmitter that transmits a constant pattern, a radio receiver, and a processing unit.